1. Field of the Invention
The present invention relates to handover of user equipment between different communication areas, and particularly to a method for performing a handover between MBSFN and non-MBSFN areas as well as user equipment therefor, which can provide continuous MBMS service when the user equipment moves between different communication areas.
2. Description of Prior Art
The 3GPP launched the 3G LTE (Long Term Evolution) in 2005 in which evolved access technologies, such as E-UTRA, and evolved access networks, such as E-UTRAN, are utilized to provide better support for carriers and users' increasing requirements. In the LTE, it is clearly advanced that the evolved MBMS (Multimedia Broadcast Multicast Service) services (E-MBMS) shall be supported. MBMS is a service introduced in 3GPP Release 6 and refers to a point-to-multipoint wireless communication service for transmitting data from one data source to a plurality of users, so as to achieve an evolution of network resource including a core network and an access network while serving as many multimedia users with the same requirements as possible by using as little resources as possible. The introduction of MBMS adds three logic channels into the standard, i.e. a MCCH (MBMS control channel), a MTCH (MBMS traffic channel) and a MSCH (MBMS scheduling channel). The MCCH channel always exists in a cell since it is required to timely notify UEs of control information related to MBMS service.
As an evolved technology from the MBMS, one of the most important features of E-MBMS lies in that its service data are combined using MBSFN (MBMS Single Frequency Network) in an air structure. That is, for the same service, data transmitted from difference base stations are designed to transmit the same content at the same time. In this way, a UE may receive, over the air interface, a natural superposition of physical signals having the same content from a plurality of base stations, which leads to a multiplied reception SNR (Signal-to-Noise). Such a set of cells that can implement MBSFN transmission is called a MBSFN area. In order to implement MBSFN transmission of service data, many forms may be adopted for respective service data in the access network. A single-cell transmission mode is adopted in the access network for services not participating in the MBSFN transmission.
Further, RAN2#58 has already proposed that the transmission of MBMS service in E-UTRAN may be either a single-cell transmission or a multi-cell (MBSFN) transmission. As stated in the above, the multi-cell transmission is characterized by simultaneous transmission of MBMS service from multiple cells within a MBSFN Area and support to combination of MBMS transmissions from multiple cells. On the contrary, the single-cell transmission is characterized in that MBMS service is transmitted only within the coverage of a specific cell and combination of MBMS transmissions from multiple cells is not supported. Therefore, when UE moves, especially between MBSFN and non-MBSFN areas, the UE is required to perform a handover and a transmission mode switching operation so as to provide continuous MBMS service.